Signal receiver



Oct. 8, 1929. J. F. FARRINGTON ET AL 1,730,605

SIGNAL nacsxvsn Filed July 27, 1923 Patented Oct. 8, 1929 UNITED STATESPATENT OFFICE JOHN F. FARRINGTON, OF FLUSIIING, NEW YORK, AND EDWIN H.SMTZTHE, OF CHI= GAGO, ILLINOIS, ASSIGNORS TO ELECTRIC COMPANY,INCORPORATED, OF NEW YORK, N. Y., A CORPORA'IIQN OF NEW YORK SIGNALRECEIVER This invention relates to a signal receiver.

More particularly, the invention relates to a double detection signalreceiver wherein a signal modulated high frequency wave is detected toyield a signal modulated intermediate frequency wave, which is thendetected to yield the signal.

An object of this invention is to improve and simplify double-detectionreceiver cir cuits. I

In such systems ofthe prior art, the signal modulated high frequencywave is impressed upon a frequency converter which steps down theincoming wave to an intermediate frequency wave modulated in accordancewith the signal. Thes-ignal modulated interme diate frequency wave isthenimpressed upon a second frequency converter or detector which yieldsthe signal.

In accordance with one feature of this invention the same frequencyconverter or detector circuit is employed both for combining thereceived signal modulated waves with waves from a local source and fordetecting the resulting combination products to yield the signal.

In accordance with another feature of the invention the single frequencyconverting 0r detecting circuit is of the balanced or pushpull type, theintermediate frequency circuit being connected between the input andoutput circuits thereof, the connections being made symmetrically withrespect to one circuit and differentially with respect to the other inorder 1 to eliminate any singingeffects.

According to an auxiliary feature of the invention, the intermediatefrequency wave modulated in accordance with the signal is selectivelyamplified before being impressed upon the detector.

Nhile the invention is illustrated as ap plied to a radio receiver itwill be understood that it may find application in other signalreceivers such, for example, as are employed in carrier wave systemshaving conductive circuits between stations.

In the drawings:

1 shows diagrammatically a radio signal receiver wherein the signalmodulated radio waves are impressed upon the individ- 1923. Serial No.654,104.

ual branches of the input circuits of a I balanced detector, and wavesfrom a local source and the detected intermediate frequency waves areimpressed upon the'common branch of the input circuits.

Fig. 2 shows diagrammatically a radio signal receiver wherein the wavesfrom the local source are impressed upon the individual branches of theinput circuits of a bal anced detector and the incoming signal modulatedradio waves and the intermediate frequency waves are impressed upon thecommon branch of the input circuits.

Fig. 3 shows diagrammatically a radio signal receiver wherein theincoming signal modulated radio waves and the waves from the localsource are impressed upon the com.-

mon branch of the input circuits of a balanced detector and the detectedintermediate frequency waves are impressed upon the individual branchesof the input circuits.

Fig. 4 shows diagrammatically a radio signal receiver wherein theincoming signal modulated radio waves, the waves from the local sourceand the detected intermediate frequency waves are impressed upon theindividual branches of the input circuits of a balanced detector.

' The radio receiver of Fig. 1 comprises an antenna 1, a balanceddetector D, a band filter IBF, a low pass filter LPF, and amplifiers Aand A. I

The balanced detector may be of any well known type, such, for example,as that disclosed in United States patent to Carson No. 1,343,308, June15, 1920.

This balanced detector has two three-electrode valves 2 and 2. Theauxiliary electrodes or grids of these valves are connected to theterminals of the secondary winding of an input transformer 3, whoseprimary winding is included in circuit with the antenna 1. The mid-pointof the secondary winding of transformer 3 is connected through thesecondary windings of transformers 4: and 5, to the cathodes of the twovalves. The anodes of the two valves are connected to the terminals ofthe primary winding of an output transformer 6. The mid-point of thisprimary winding is connected through the primary winding of atransformer 7 to the cathodes of the two valves. The secondary windingof the outputtransformer is connected through the band filter IBF to theinput of amplifier A.

The band filter IBF is, of the type disclosed in United States patent toCampbell No. 1,227,113, May 22, 1917. This filter is designed to passcurrents of a frequency intermediate the incoming radio frequency andthe signal frequencies and currents within either the upper or lowerside band of that intermediate frequency, and to suppress currents ofall other frequencies. i

The low pass filter LPF is of the type disclosed in the Campbell patent,supra. It is designed to pass currents of the signal frequencies and tosuppress currents of higher frequencies.

The amplifiers A and A may be of any Well known type such, for example,as the threeelectrode-electronic valve shown in Fig.28 of the articleentitled Carrier cur rent telephony and telegraphy by Colpitts andBlackwell, published in the Transactions of American Institute ofElectrical Engineers, Vol. 40, 1921.

The output circuit of amplifier A is connected to the primary winding oftrans former 5.

A local source 0 of oscillations is connected to the primary winding oftransformer 4. The secondary winding of transformer 7 is connected tothe low pass filter LPF, and the output circuit of amplifier A5 isconnected to a signal receiving device such as a telephone receiver 8.

The incoming radio waves may have a frequency of 7 00,000 cycles and thelocal source 0 may supply waves of 650,000 cycles.

The operation of the radio receiver shown in Fig. 1 is as follows Thedesired incoming radio waves modulated in accordance with signals whichmay be speech are intercepted by the antenna 1 and selected by theantenna circuit which, according to customary practice, may be tuned forthat purpose. The selected signal modulated radio waves are impressedthrough transformer 3 upon the input circuits of the balanced detectorD. The signal modulated radio waves interact with the waves from localsource 0 in the detector D which produces in the secondary winding ofoutput transformer 6 a current having components with frequencies equalto the sum and difierence of the radio and locally in1- pressedfrequencies, each modulated by the signal frequencies.

The signal. modulated radio waves arereproduced in the secondary windingof outputtransformer 6. The band filter TBF prevents the passage of suchwaves to the ampli- The waves from local source 0 impressed upon thecommon branch of the detector in= put circuits are balanced out in theprimary winding of the output transformer and consequently do not appearin the secondary winding thereof. While the waves from local source 0are reproduced in the secondary winding of transformer 7, the low passfilter LPF prevents the passage of such waves to the amplifier A.

Currents of an intermediate frequenc modulated by signals are selectedby the band filter IBF and are impressed upon the amplifier A. Thisintermediate frequency is the difference between the incoming radiofrequency and the frequency supplied from the local source 0.

The intermediate frequency currents modulated by speech are amplified byamplifier A and are impressed through transformer 5 upon the commonbranch of the input circuits of the detector 1). Frequency components ofthe detected signal modulated intermediate frequency currents areproduced in the output circuits of the detector. Among these componentsa band of frequencies within the signal or speech range which appears inthe common branch of the output circuits and is impressed throughtransformer 7 upon the circuit including the low pass filter. This lowpass filter LPF passes this band of frequencies and suppresses currentsof higher frequencies. The band of frequencies passed bythe low passfilter and amplified by amplilier A are impressed upon the receiver 8.

The radio receiver of Fig. 2 is similar to that of Fig. l differingtherefrom merely in the manner of connecting the antenna and the localsource of oscillations to the input circuits of the balanced detector.The antenna 1 is coupled to the common branch of the input circuits ofthe detector D by means of transformer 4, while the local source ofoscillations O is connected to the individual branches of the inputcircuits by means of transformer 3.

The operation of this radio receiver is similar to that of Fig. 1. I

Currents having frequency components equal to the sum and difference ofthe radio frequency and the frequency from local source 0, eachmodulated 'by the signal are produced in the secondary winding of theoutput transformer 6. One of these components, such, for example, as thesignal modulated difference frequency, is selected by band filter IBFand impressed upon the amplifier A. The signal modulate-d radiofrequency, impressed on the common branch of the input circuits isbalanced out in the primary winding of output transformer 6, andtherefore is not reproduced in the secondary winding. The local sourcefrequency impressed upon the individual branches of the inputcircuits isreproduced in the secondary winding of the output transformer, but issuppressed by the band filter IBF. During the process of detecting thesignal modulated radio frequency to yield the signal modulatedintermediate frequency, the signal frequency currents of small amplitudeare obtained direct from the incoming waves and are impressed throughtransformer 7 and low pass filter LPF onto the amplifier A. Theamplified signal modulated intermediate frequency currents are impressedupon the common branch of the de tector input circuits so as to yieldthe amplified signal frequency currents in the same way as in thereceiverof Fig. 1.

I The radio receiver of Fig. 3 employs a balanced detector D of the typedisclosed in United States patent to Hartley No. 1,419,562, June 13,1922. v v

The incoming signal modulated radio waves and the oscillations from thelocal source are impressed upon'the common branch of the detector inputcircuits through transformers 1 and 5 respectively. The amplified signalmodulated intermediate frequency is impressed upon the individualbranches of the detector input circuits through transformer 3. Theanodes of the detector electronic valves 22 and 22 are connected to oneterminal of the primary winding of output transformer 9, the otherterminal of which is connected to the cathodes of the two valves. Thesecondary Winding of the output transformer 9 has connected thereto theband filter IBF and the low pass filter LPF, whose input circuits may beconnected in series as shown.

The operation of the radio receiver of Fig. 3 may be explained asfollows:

The incoming signal modulated radio waves and the waves from localsource 0 impressed upon the common branch of the detector input circuitsinteract to produce in the secondary winding of output transformer 9currents having the following frequency components (1) Radio frequency.

(2) Local source frequency.

(3) Radio frequency modulated by the signal.

(4) Sum of radio and local source frequencies modulated by the signal.

(5) Difference between radio and local source frequencies modulated bythe signal.

(6) Harmonics of (4) and (5).

(7) Signal frequencies (small amplitude).

Due to the action of band filter IBF, only currents of frequencycomponent (4:) or (5) pass therethrough and are impressed upon theamplifier A. Likewise, due to the action of low pass filter LPF, onlythe signal frequency currents pass therethrough and are impressed uponthe amplifier A.

The amplified signal modulated intermediate frequency currents fromamplifier A are impressed through transformer 3 upon the individualbranches of the detector input circuits. The resulting currents in thesecond-- detector input circuits.

ary winding of output transformer 9 have the following frequencycomponents:

(A) Second harmonic of intermediate fre quency.

(B Amplified signal frequencies.

. The band filter IBF suppresses currents of all these frequencycomponents and the low pass filter LPF suppresses all but the amplifiedsignal frequency currents which pass therethrough and are impressed uponthe amplifier A.

The radio receiver of Fig. a is similar to that of Fig. 3, with thisdifference: The incoming signal modulated radio waves, the waves fromthe local source 0 and the signal modulated intermediate frequency wavesare impressed upon the individual branches of the detector inputcircuits.

The antenna is coupled to the detector by means of a. transformer 10having three primary windings, one of which is in series with theantenna. The local source 0 is connected to a second primary winding ofthis transformer 10, while the output circuit of amplifier A isconnected to the third primary winding. The secondary winding oftransformer 10 is connected to the primary winding of transformer 3.

Y The radio receiver of Fig. 24 operates as follows: 7

The incoming signal modulated radio waves and the waves from the localsource are ime pressed upon the individual branches of the The currentsproduced in the secondary winding of output transformer 9 have thefollowing frequency components Second harmonic of radio frequency.

Second harmonic of local source frequency. Sum of radio and local sourcefrequencies modulated by the signal.

Difference between radio and local source frequencies modulated by thesignal.

Signal frequencies (small amplitude).

The band filter IBF passes either the signal modulated sum or differencefrequency currents, preferably the latter, which are impressed upon theamplifier A and suppresses currents of all other, frequencies.

The low pass filter LPF passes only the signal frequency currents whichare then impressed upon amplifier A.

The amplified signal modulated intermediate frequency currents areimpressed upon the individual branches of the detector input circuits toyield the signal in the output cir-' cuit thereof in the same manner asin the radio receiver of Fig. 3.

The amplifier A is adjusted to give comparatively large gain in thesignal modulated intermediate frequency waves, which is possible becausesuch waves are prevented from re-entering the amplifier after beingimpressed upon the detector input circuits.

Consequently singing-is prevented.

Since the signal modulated intermediate frequency waves are greatlyamplified by the amplifier A, a greatly amplified signal is ob tainedfrom detection of such amplified signal modulated intermediate frequencywaves. Therefore the amplitude of the signal resulting from doubledetection is many times greater than that of the signal resulting fromdirect detection of the incoming signal modulated high frequencywaves.Consequently the double detection receivers shown in the drawings arehighly selective, since any low frequency currents resulting from directdetection of any incoming interfering high frequency waves arenegligible compared to the desired amplified signal resulting fromdouble detection. 4

The invention set forth herein is obviously susceptible of various othermodifications and adaptations.

The invention claimed is:

1. A double detection signal receivercomprising a detector having inputand output circuit, means for impressing an incoming signal modulatedhigh frequency wave upon the input circuit, alocal source of waves,means for impressing waves from the local source upon the input circuit,means in the output circuit to pass a signal modulated intermediatefrequency wave and to suppress waves of all other frequencies, anamplifier having its input circuit coupled to the he quencydiscriminating means and its output circuit coupled to the detectorinput circuit, a signal responsive device, and a low pass filter betweensaid device and the detector output circuit.

2. The method of operating a double de tection signal receiver employinga single detector circuit, which comprises impressing an incoming signalmodulated high frequency wave upon the detector and therein convertingsuch incoming wave into a signal modulated wave of a lower frequency,and impressing such signal modulated lower frequency wave upon thedetector and therein detecting the same to yield the signal.

3. The method ofoperating a double detection signal receiver employing asingle detector circuit, which comprises impressing an incoming signalmodulated high frequency wave upon .the detector and producing a wavehaving frequency components including a lower frequency modulated inaccordance with the signal; selecting, amplifying and impressing thesignal. modulated lower frequency wave upon the detector and producingin said detector circuit a wave having frequency components includingthe signal frequencies, and selecting the signal frequencies.

4;. A signal receiver comprising a frequency converting or detectingdevice having input and output circuits, means to impress an incomingsignal modulated high frequency wave upon the input circuit and producein the output circuit a lower frequency wave modulated in accordancewith the signal, means to amplify the signal modulated lower frequencywave and impress such amplified Wave upon said input circuit so as toproduce in the output circuit a wave of the signal freuencies, a signalreceiving device coupled to said output circuit, and frequencydiscriminating means in said output circuit to direct the signalmodulated lower frequency wave to its amplifying means and to direct thesignal frequency wave to the receiving device.

5. A signal receiver comprising a balanced detector having input andoutput circuits, 2.

local source of waves, means to impress a wave from the local source anda signal modulated high frequency wave upon the input circuit so astoproduce in the output circuit a signal modulated wave having a frequencywhich is the difierence between the high frequency wave and thefrequency of the wave from the local source, means coupled to the outputcircuit to select, amplify, and impress such signal modulated differencefrequency wave upon the input circuit so as to produce in the outputcircuit the signal frequency wave, a signal. receiving device, and meanscoupled to the output circuit to select and impress the signal frequencywave upon the signal receiving device.

6. In combination a pair of three-electrode electric discharge devicesconnected in pushpull relation between an input circuit and an outputcircuit so that waves supplied to one portion of said input circuit willnot appear in one portion of said output circuit, means for supplyingsignal modulated waves to said input circuit, means for supplying tosaid input circuit a carrier or heterodyne wave which combines with saidfirst wave to pro duce super-audible frequency combination products insaid output circuit, amplifying means interconnecting said portions ofsaid input and output circuits for feeding back said combinationproducts to said input circuit whereby the signal wave is detected, andmeans responsive to the signal wave connected to said output circuit.

7. A double detection receiving system comprising a pair ofthree-electrode electric discharge detectors, a source of signalmodulated waves, a local source of waves, means for impressingwaves fromsaid sources upon said detectors in push-pull relation for producing inthe output thereof signal modulated combination products of said waves,means for selectively amplifying said signal modulated combinationproducts to the exclusion of waves of other frequencies connecteddifferentially to the outputs of said detectors, means, for impressingsaid amplified combination products upon said detectors in parallel fordetecting the signal wave, and means responsive to the detected signalwave connected to the output-s of said detectors in parallel.

8. A double detection receiver comprising a pair of three-electrodeelectric discharge detectors connected in push-pull relation between aninput circuit and an output circuit, a source of signal modulated waves,a local source of Waves, means for impressing waves from said sourcesupon said input circuit to produce in said output circuit combinationproducts thereof, an amplifier having a frequency selectivecharacteristic for selectively amplifying said combination products,said amplifier having an input circuit connected to the detector outputcircuit and an output circuit connected to the detector input circuitwhereby the amplified combination products are impressed upon saiddetector and detected toproduce the signal, the connection of saidamplifier to the detector input and output circuits being, with respectto said detectors, symmetrical in one of said circuits and differentialin the other of said circuits, and a circuit selectively responsive tothe signal waves connected to the output circuit.

9. A double detection receiver comprising a pair of three-electrodeelectric discharge devices, each having an anode, a cathode and acontrol electrode, said devices being connected in push-pull relationbetween an input and an output circuit, each of said circuits having aportion common to said cathodes, said input circuit having proportionsindividual to said control electrodes, and said output circuit havingproportions individual to said anodes, a source of signal modulatedwaves, a local source of waves, means for impressing waves from saidsources upon said input circuit to produce in the individual portions ofthe output circuit difference frequency combination products of saidwaves, a frequency selective amplifier having its input connected toreceive waves from said individual portions of the output circuit forselectively amplifying said difference frequency combination productsand having its output connected to supply the amplified combinationproducts to the common input portion of the input circuit whereby thecombination products are detected to yield the 7 signal, and a circuitselectively responsive to the detected signal waves connected to thecommon portion of the output circuit;

In witness whereof, I hereunto subscribe my name this 13th day of July,A. D. 1923. JOHN F. FARRINGTON. In witness whereof, I hereunto subscribemy name this 23rd day of July, A. D. 1923. EDWIN H. SMYTHE.

